1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___ALGORITHM_COPY_BACKWARD_H
10#define _LIBCPP___ALGORITHM_COPY_BACKWARD_H
11
12#include <__algorithm/copy_move_common.h>
13#include <__algorithm/iterator_operations.h>
14#include <__algorithm/min.h>
15#include <__config>
16#include <__iterator/segmented_iterator.h>
17#include <__type_traits/common_type.h>
18#include <__type_traits/is_copy_constructible.h>
19#include <__utility/move.h>
20#include <__utility/pair.h>
21
22#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
23#  pragma GCC system_header
24#endif
25
26_LIBCPP_PUSH_MACROS
27#include <__undef_macros>
28
29_LIBCPP_BEGIN_NAMESPACE_STD
30
31template <class _AlgPolicy, class _InIter, class _Sent, class _OutIter>
32_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InIter, _OutIter>
33__copy_backward(_InIter __first, _Sent __last, _OutIter __result);
34
35template <class _AlgPolicy>
36struct __copy_backward_loop {
37  template <class _InIter, class _Sent, class _OutIter>
38  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
39  operator()(_InIter __first, _Sent __last, _OutIter __result) const {
40    auto __last_iter          = _IterOps<_AlgPolicy>::next(__first, __last);
41    auto __original_last_iter = __last_iter;
42
43    while (__first != __last_iter) {
44      *--__result = *--__last_iter;
45    }
46
47    return std::make_pair(std::move(__original_last_iter), std::move(__result));
48  }
49
50  template <class _InIter, class _OutIter, __enable_if_t<__is_segmented_iterator<_InIter>::value, int> = 0>
51  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
52  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
53    using _Traits = __segmented_iterator_traits<_InIter>;
54    auto __sfirst = _Traits::__segment(__first);
55    auto __slast  = _Traits::__segment(__last);
56    if (__sfirst == __slast) {
57      auto __iters =
58          std::__copy_backward<_AlgPolicy>(_Traits::__local(__first), _Traits::__local(__last), std::move(__result));
59      return std::make_pair(__last, __iters.second);
60    }
61
62    __result =
63        std::__copy_backward<_AlgPolicy>(_Traits::__begin(__slast), _Traits::__local(__last), std::move(__result))
64            .second;
65    --__slast;
66    while (__sfirst != __slast) {
67      __result =
68          std::__copy_backward<_AlgPolicy>(_Traits::__begin(__slast), _Traits::__end(__slast), std::move(__result))
69              .second;
70      --__slast;
71    }
72    __result = std::__copy_backward<_AlgPolicy>(_Traits::__local(__first), _Traits::__end(__slast), std::move(__result))
73                   .second;
74    return std::make_pair(__last, std::move(__result));
75  }
76
77  template <class _InIter,
78            class _OutIter,
79            __enable_if_t<__has_random_access_iterator_category<_InIter>::value &&
80                              !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
81                          int> = 0>
82  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
83  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
84    using _Traits           = __segmented_iterator_traits<_OutIter>;
85    auto __orig_last        = __last;
86    auto __segment_iterator = _Traits::__segment(__result);
87
88    // When the range contains no elements, __result might not be a valid iterator
89    if (__first == __last)
90      return std::make_pair(__first, __result);
91
92    auto __local_last = _Traits::__local(__result);
93    while (true) {
94      using _DiffT = typename common_type<__iter_diff_t<_InIter>, __iter_diff_t<_OutIter> >::type;
95
96      auto __local_first = _Traits::__begin(__segment_iterator);
97      auto __size        = std::min<_DiffT>(__local_last - __local_first, __last - __first);
98      auto __iter        = std::__copy_backward<_AlgPolicy>(__last - __size, __last, __local_last).second;
99      __last -= __size;
100
101      if (__first == __last)
102        return std::make_pair(std::move(__orig_last), _Traits::__compose(__segment_iterator, std::move(__iter)));
103      --__segment_iterator;
104      __local_last = _Traits::__end(__segment_iterator);
105    }
106  }
107};
108
109struct __copy_backward_trivial {
110  // At this point, the iterators have been unwrapped so any `contiguous_iterator` has been unwrapped to a pointer.
111  template <class _In, class _Out, __enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
112  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
113  operator()(_In* __first, _In* __last, _Out* __result) const {
114    return std::__copy_backward_trivial_impl(__first, __last, __result);
115  }
116};
117
118template <class _AlgPolicy, class _BidirectionalIterator1, class _Sentinel, class _BidirectionalIterator2>
119_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_BidirectionalIterator1, _BidirectionalIterator2>
120__copy_backward(_BidirectionalIterator1 __first, _Sentinel __last, _BidirectionalIterator2 __result) {
121  return std::__dispatch_copy_or_move<_AlgPolicy, __copy_backward_loop<_AlgPolicy>, __copy_backward_trivial>(
122      std::move(__first), std::move(__last), std::move(__result));
123}
124
125template <class _BidirectionalIterator1, class _BidirectionalIterator2>
126inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _BidirectionalIterator2
127copy_backward(_BidirectionalIterator1 __first, _BidirectionalIterator1 __last, _BidirectionalIterator2 __result) {
128  static_assert(std::is_copy_constructible<_BidirectionalIterator1>::value &&
129                    std::is_copy_constructible<_BidirectionalIterator1>::value,
130                "Iterators must be copy constructible.");
131
132  return std::__copy_backward<_ClassicAlgPolicy>(std::move(__first), std::move(__last), std::move(__result)).second;
133}
134
135_LIBCPP_END_NAMESPACE_STD
136
137_LIBCPP_POP_MACROS
138
139#endif // _LIBCPP___ALGORITHM_COPY_BACKWARD_H
140